1. Technical Field of the Invention
The present invention relates to the 100 Base-T Fast Ethernet and, more particularly, to the transport of fast ethernet data on optical media according to the Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) standards.
2. Discussion of Related Art
The present international standard ISO/IEC 8802-3, corresponding to ANSI/IEEE Standard 802.3u-1995, provides a 100 Base-T, i.e., 100 Mbps, fast ethernet definition for Carrier Sense Multiple Access With Collision Detection (CSMA/CD) access method and physical layer specifications. The standard provides for the interface of the 100 Base-T fast ethernet with a SONET synchronous payload envelope (SPE) utilizing only two-thirds of the payload capacity thereof, thereby utilizing the transport capacity of the SONET SPE/SDH VC signal, specifically the SONET-STS-3c/SDH-VC-4, which operate at 155.520 Mbit/s (hereinafter "approximately 150 Mbps").
The synchronous optical network (SONET)/synchronous digital hierarchy (SDH) provides for various optical interface rates and formats, including super-rate services that require multiples of the basic STS-1 (for North America) rate that are mapped into an STS-Nc SPE and transported as a concatenated STS-Nc, whose constituent STS-1s are kept together. The STS-Nc is carried by an STS-M line signal, where M is greater than or equal to N. The STS-Nc is multiplexed, switched and transported through the network as a single entity. The STS-Nc consists of N.times.87 columns and 9 rows of bytes. The order of transmission is row-by-row from left to right, as shown in FIG. 27 of ANSI T1.105. Only one set of STS path overhead is required in the STS-Nc SPE. The STS-Nc SPE is carried within the STS-Nc such that the STS path overhead always appears in the first of the N STS-1s which make up the STS-Nc. For instance, an STS-3c SPE will include 3.times.87.times.9 bytes=2,349 bytes, of which 9 bytes are path overhead, and 2,340 bytes are payload capacity.
According to the above-mentioned international standard, the 100 Base-T fast ethernet, when transported on an optical network, inefficiently utilizes the transport capacity of the defined transport mechanisms. In the prior art, the unused capacity is filled with fixed stuff bytes.